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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Mycorrhizal fungi network / Mycorrhizal nutrient trade: phosphorus, nitrogen and carbon market

Mycorrhizal nutrient trade: phosphorus, nitrogen and carbon market

Fungal hyphae take up phosphorus and nitrogen and deliver them to the root at arbuscules, while the plant pays hexoses and fatty acids. The outcome ranges from mutualism to parasitism depending on soil phosphorus and light, and plant phosphorus status regulates the payment.

Boundary: where this process starts

Starts with: Extraradical hyphae take up phosphate through high-affinity transporters beyond the depletion zone

Boundary: where it ends

Ends after: Reciprocal reward and sanctioning; Hyphal growth and turnover are fuelled by plant carbon

PARTICIPANTSRESOURCESHost plantFungal hyphaeArbuscularmycorrhizalfungiRoot cortexcellsMycorrhizalfungiPhosphorusCarbonPhosphatePolyphosphateNitrogenImpact +3 of 5. Click for details and evidence.Hyphae forageImpact +3 of 5. Click for details and evidence.Plant pays carbonImpact +4 of 5. Click for details and evidence.Pi condensedImpact +4 of 5. Click for details and evidence.Carried to arbusculeImpact +4 of 5. Click for details and evidence.Pi crosses membraneImpact +3 of 5. Click for details and evidence.N also taken upImpact +3 of 5. Click for details and evidence.Nitrogen delivered at the saImpact -3 of 5. Click for details and evidence.Cost accumulatesImpact +4 of 5. Click for details and evidence.60% P-limited soil, good ligImpact 01 of 5. Click for details and evidence.25% intermediate fertilityImpact -3 of 5. Click for details and evidence.15% high P or low lightImpact +3 of 5. Click for details and evidence.Plant P risesImpact -2 of 5. Click for details and evidence.P already highImpact -4 of 5. Click for details and evidence.↻ balances · strong · 0.5 Higher plant P dowImpact +4 of 5. Click for details and evidence.Carbon fuels hyphaeImpact +4 of 5. Click for details and evidence.↻ reinforces · strong · 0.4 More hyphae meanImpact +3 of 5. Click for details and evidence.Plant tests deliveryImpact +3 of 5. Click for details and evidence.Trade settledImpact +2 of 5. Click for details and evidence.Hyphal turnover feeds soil cImpact -3 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.Impact 01 of 5. Click for details and evidence.Extraradical hyphae take up phosphate through high-affinity transporters beyond the depletion zone: uses up Phosphorususes upExtraradical hyphae take up phosphate through high-affinity transporters beyond the depletion zone: uses up Phosphateuses upPhosphate is condensed into polyphosphate and moved along hyphae by cytoplasmic streaming: uses up Phosphorususes upPhosphate is condensed into polyphosphate and moved along hyphae by cytoplasmic streaming: makes PolyphosphatemakesPolyphosphate is hydrolysed in arbuscules and phosphate is released into the periarbuscular space: makes PhosphatemakesPlant phosphate transporter PT4 takes up phosphate across the periarbuscular membrane: uses up Phosphateuses upNitrogen: ammonium assimilated into arginine in hyphae, carried, then broken down in the arbuscule: uses NitrogenPlant delivers hexoses and fatty acids (lipids) to the fungus, which cannot make its own fatty acids: uses CarbonCarbon cost to the plant: roughly 4-20% of fixed carbon goes to the fungal partner: uses up Carbonuses upNet outcome depends on soil phosphorus and light: uses PhosphorusNet outcome depends on soil phosphorus and light: uses CarbonMutualism: P supplied exceeds carbon cost, growth rises: uses PhosphorusMutualism: P supplied exceeds carbon cost, growth rises: uses CarbonNeutral: carbon cost and phosphorus benefit roughly cancel: uses PhosphorusNeutral: carbon cost and phosphorus benefit roughly cancel: uses CarbonParasitism: plant has abundant P and carbon cost becomes a net loss: uses PhosphorusParasitism: plant has abundant P and carbon cost becomes a net loss: uses CarbonPlant phosphorus status falls or rises and systemically regulates colonization: uses PhosphorusHyphal growth and turnover are fuelled by plant carbon: uses up Carbonuses upReciprocal reward and sanctioning: uses PhosphorusReciprocal reward and sanctioning: uses Carbontaken up by hyphaePhosphorus: taken up by hyphaeabsorbed by hyphaltransportersPhosphate: absorbed by hyphal transportersstored as polyphosphatePhosphorus: stored as polyphosphatemoved by cytoplasmicstreamingPolyphosphate: moved by cytoplasmic streamingreleased intoperiarbuscular spacePhosphate: released into periarbuscular spacetaken up by transporterPhosphate: taken up by transporterassimilated intoarginineNitrogen: assimilated into argininetransferred to fungalpartnerCarbon: transferred to fungal partnerdiverted to fungalpartnerCarbon: diverted to fungal partneravailability setsoutcomePhosphorus: availability sets outcomeallocation determinesnet effectCarbon: allocation determines net effectsupplied in excess ofcostPhosphorus: supplied in excess of costoutweighed by phosphorusgainCarbon: outweighed by phosphorus gainbalanced against carboncostPhosphorus: balanced against carbon costbalanced againstphosphorus gainCarbon: balanced against phosphorus gainabundant and unneededPhosphorus: abundant and unneededbecomes net loss toplantCarbon: becomes net loss to plantregulates colonizationlevelPhosphorus: regulates colonization levelfuels hyphal growthCarbon: fuels hyphal growthrewarded or withheldPhosphorus: rewarded or withheldrewarded or withheldCarbon: rewarded or withheldStart: Hyphae holdnutrients, plant holdscarbonSTARTStart: Hyphae hold nutrients, plant holds carbonEnd: Trade settled andbalance checkedENDEnd: Trade settled and balance checkedExtraradical hyphaetake up phosphatethrough high-affini…📄2Extraradical hyphae take up phosphate through high-affinity transporters beyond the depletion zonePhosphate is condensedinto polyphosphate andmoved along hyphae …📄1Phosphate is condensed into polyphosphate and moved along hyphae by cytoplasmic streamingPolyphosphate ishydrolysed inarbuscules a…📄1Polyphosphate is hydrolysed in arbuscules and phosphate is released into the periarbuscular spacePlant phosphatetransporter PT4 takesup phosphate across t…📄1Plant phosphate transporter PT4 takes up phosphate across the periarbuscular membraneNitrogen: ammoniumassimilated intoarginine in hypha…📄1Nitrogen: ammonium assimilated into arginine in hyphae, carried, then broken down in the arbusculePlant delivers hexosesand fatty acids(lipids) to the fungu…👍1📄2Plant delivers hexoses and fatty acids (lipids) to the fungus, which cannot make its own fatty acidsCarbon cost to theplant: roughly 4-20% offixed carbon goes …👍1📄2Carbon cost to the plant: roughly 4-20% of fixed carbon goes to the fungal partnerNet outcome depends onsoil phosphorus andlight📄2Net outcome depends on soil phosphorus and lightMutualism: P suppliedexceeds carbon cost,growth rises📄1Mutualism: P supplied exceeds carbon cost, growth risesNeutral: carbon costand phosphorus benefitroughly cancel📄1Neutral: carbon cost and phosphorus benefit roughly cancelParasitism: plant hasabundant P and carboncost becomes a net loss📄1Parasitism: plant has abundant P and carbon cost becomes a net lossPlant phosphorus statusfalls or rises andsystemically regulat…📄1Plant phosphorus status falls or rises and systemically regulates colonizationHyphal growth andturnover are fuelled byplant carbon📄1Hyphal growth and turnover are fuelled by plant carbonReciprocal reward andsanctioning↘📄1Reciprocal reward and sanctioning
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
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Inside this process

Reciprocal reward and sanctioning

Plants and fungi reward partners who deliver more and penalize poor ones: plants give more carbon to roots hosting generous fungi and fungi give more phosphorus to roots paying more carbon. Arbuscules of low-delivery partners degenerate.

Every step, with its evidence

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Extraradical hyphae take up phosphate through high-affinity transporters beyond the depletion zone
Fungal hyphaePhosphate transportersPhosphorusPhosphate
Evidence (2) · added by Ember
  • Harrison & van Buuren 1995, A phosphate transporter from the mycorrhizal fungus Glomus versiforme, Nature 378:626-629: First fungal Pi transporter (GvPT) cloned from Glomus versiforme; expressed in extraradical hyphae with high affinity (confidence 0.85)
  • Smith & Smith 2011, Roles of arbuscular mycorrhizas in plant nutrition and growth, Annu Rev Plant Biol 62:227-250: Hyphae reach beyond the root depletion zone, which is a few mm for P (confidence 0.75)
Phosphate is condensed into polyphosphate and moved along hyphae by cytoplasmic streaming
Fungal hyphaePhosphorusPolyphosphate
Evidence (1) · added by Ember
  • Ezawa et al. 2004, Rapid accumulation of polyphosphate in extraradical hyphae of an AM fungus, New Phytologist 161:387-392: Extraradical hyphae rapidly accumulate polyphosphate after Pi application, a mobile storage form (confidence 0.8)
Polyphosphate is hydrolysed in arbuscules and phosphate is released into the periarbuscular space
ArbusculesRoot cortex cellsPhosphate
Evidence (1) · added by Ember
  • Smith & Smith 2011, Roles of arbuscular mycorrhizas in plant nutrition and growth, Annu Rev Plant Biol 62:227-250: Pi is released at the interface and taken up by the plant (confidence 0.75)
Plant phosphate transporter PT4 takes up phosphate across the periarbuscular membrane
Root cortex cellsHost plantPhosphate
Evidence (1) · added by Ember
  • Javot et al. 2007, A Medicago truncatula phosphate transporter indispensable for the arbuscular mycorrhizal symbiosis, PNAS 104:1720-1725: Medicago MtPT4 is required for symbiotic Pi uptake; mutants lose arbuscules (confidence 0.9)
Nitrogen: ammonium assimilated into arginine in hyphae, carried, then broken down in the arbuscule
Fungal hyphaeNitrogenAmmoniumArginine
Evidence (1) · added by Ember
  • Govindarajulu et al. 2005, Nitrogen transfer in the arbuscular mycorrhizal symbiosis, Nature 435:819-823: Nitrogen moves in AM hyphae as arginine and is released as ammonium in the root, 15N tracing (confidence 0.85)
Plant delivers hexoses and fatty acids (lipids) to the fungus, which cannot make its own fatty acids
Host plantArbuscular mycorrhizal fungiSugarsLipidsCarbon
Evidence (2) · added by Ember
  • Jiang et al. 2017, Plants transfer lipids to sustain colonization by mutualistic mycorrhizal and parasitic fungi, Science 356:1172-1175: Plants transfer lipids to AM fungi (confidence 0.9)
  • Luginbuehl et al. 2017, Fatty acids in arbuscular mycorrhizal fungi are synthesized by the host plant, Science 356:1175-1178: Fungal fatty acids are synthesized by the host plant (confidence 0.9)
Carbon cost to the plant: roughly 4-20% of fixed carbon goes to the fungal partner
Host plantCarbon
Evidence (2) · added by Ember
  • Smith & Read 2008, Mycorrhizal Symbiosis, 3rd ed., Academic Press: Reviews carbon costs of mycorrhizas; published estimates of 4-20% of net photosynthate depending on plant and conditions (confidence 0.55)
  • Jakobsen & Rosendahl 1990, Carbon flow into soil and external hyphae from roots of mycorrhizal cucumber plants, New Phytologist 115:77-83: Mycorrhizal cucumber allocated additional carbon to roots and external hyphae (confidence 0.55)
⑂ Net outcome depends on soil phosphorus and light
Host plantMycorrhizal fungiPhosphorusCarbon
Evidence (2) · added by Ember
  • Johnson, Graham & Smith 1997, Functioning of mycorrhizal associations along the mutualism-parasitism continuum, New Phytologist 135:575-585: Mycorrhizal association ranges from mutualism to parasitism with soil fertility (confidence 0.8)
  • Hoeksema et al. 2010, A meta-analysis of context-dependency in plant response to inoculation with mycorrhizal fungi, Ecology Letters 13:394-407: Meta-analysis: plants respond more where P is low and N is not limiting; shares are estimates (confidence 0.5)
Mutualism: P supplied exceeds carbon cost, growth rises
Host plantPhosphorusCarbon
Evidence (1) · added by Ember
  • Hoeksema et al. 2010, A meta-analysis of context-dependency in plant response to inoculation with mycorrhizal fungi, Ecology Letters 13:394-407: Positive growth response in P-limited soils (confidence 0.7)
Neutral: carbon cost and phosphorus benefit roughly cancel
Host plantCarbonPhosphorus
Evidence (1) · added by Ember
  • Johnson, Graham & Smith 1997, Functioning of mycorrhizal associations along the mutualism-parasitism continuum, New Phytologist 135:575-585: Neutral outcomes occur at intermediate fertility (confidence 0.6)
Parasitism: plant has abundant P and carbon cost becomes a net loss
Host plantCarbonPhosphorus
Evidence (1) · added by Ember
  • Johnson, Graham & Smith 1997, Functioning of mycorrhizal associations along the mutualism-parasitism continuum, New Phytologist 135:575-585: Mycorrhizal parasitism with high P and low light (confidence 0.65)
Plant phosphorus status falls or rises and systemically regulates colonization
Host plantPhosphorus
Evidence (1) · added by Ember
  • Breuillin et al. 2010, Phosphate systemically inhibits development of arbuscular mycorrhiza in Petunia hybrida, New Phytologist 185:1016-1030: High plant P systemically represses arbuscular mycorrhiza development and function genes (confidence 0.8)
Hyphal growth and turnover are fuelled by plant carbon
Fungal hyphaeCarbon
Evidence (1) · added by Ember
  • Smith & Read 2008, Mycorrhizal Symbiosis, 3rd ed., Academic Press: External hyphae are carbon sinks that expand when carbon is supplied (confidence 0.65)
↘ Reciprocal reward and sanctioning
Host plantMycorrhizal fungiCarbonPhosphorus
Evidence (1) · added by Ember
  • Kiers et al. 2011, Reciprocal rewards stabilize cooperation in the mycorrhizal symbiosis, Science 333:880-882: Plants and fungi both reward better trading partners (reciprocal rewards) (confidence 0.9)